What is prevention?
Every day, we take steps to prevent unwanted events from happening. We wear seat belts to prevent injury. We brush our teeth to prevent cavities. While we would like to ensure some events never happen, the best we can do is reduce the chances of their happening. We all know people who brush their teeth well and still get cavities. And, we know people who always wear their seat belts who've still been hurt in a car crash. We do what we can to improve the chances of a good outcome, but we don't always have complete control.
When talking about cancer and other chronic diseases, the same thing applies. Prevention refers mainly to lowering the risk of getting a disease rather than completely eliminating the risk.
Risk factors and prevention
Cancer tends to be caused by a combination of factors. Some factors are usually under our control (like physical activity). Some are out of our control (like age) and some are still unknown. Since many factors drive risk and we can change only a few of these, we cannot completely avoid some amount of risk.
For breast cancer, most risk factors that we have some control over have only a modest effect on risk. This means that there is no one magic bullet for preventing breast cancer, but it also means there's no one factor that will cause it. Even women with a BRCA gene mutation don't have a 100 percent chance of getting breast cancer. In fact, most people diagnosed with breast cancer are at average risk, and we don’t know which factors came together to cause the cancer.
This doesn't mean that prevention is an illusion. The disease process is just so complex, it's hard to pin down how a certain set of risk factors will affect a person. However, when we look at groups of people it becomes clearer. For example, if we find that there is a 20 percent decrease in risk of breast cancer in one group of people, we can predict that there will be a 20 percent decrease in risk in a similar group of people. What we don't know is which people in the group will get the prevention benefit.
Who benefits from prevention?
It is hard to know who benefits from prevention. We know some behaviors can lower the risk of cancer. For example, non-smokers are much less likely to develop lung cancer compared to smokers. However, we do not know who prevents lung cancer by not smoking and who would have remained cancer-free even if they had smoked. So while we know that not smoking lowers the chance that a person will develop lung cancer, we do not know how great this benefit is for any one person. Further, most smokers will never be diagnosed with lung cancer and some non-smokers will. Taking steps to prevent cancer does not ensure that a person never develops the disease.
The good news is that most behaviors that are typically under our control and reduce the risk of breast cancer are part of a healthy lifestyle. Making healthy choices can have rewards beyond breast cancer prevention. Choosing a healthy lifestyle can lower the risk of other types of cancer as well as many other chronic diseases such as diabetes and heart disease.
Updated 11/06/09
